Upload any PDF and this converter will compute a SHA-256 checksum and display a 32-character truncated output (the first 16 bytes in hex).
Rename your PDF file to that 32-character string and upload it again — the converter should produce the same 32-character output, proving the file hasn’t been altered.
You can then record that 32-character string on the Bitcoin blockchain (via Notify OP_Return) as an immutable, timestamped proof that the document corresponding to that hash existed and has not been modified.